The present invention relates generally to electrochemical devices using liquid or polymer electrolytes or requiring hermetic packaging, and more particularly, to packaging and enclosures for encasing and hermetically sealing an electrolytic cell or battery.
Improvements in microelectronics have increased the demand for electrolytic cells and batteries that can be directly incorporated into electronic devices so as to produce a portable, finished package. As the improvements in microelectronics reduce the size of the electronic device, the space allotted to a power supply within such device has likewise decreased. It is therefore important to maximize the power-per-unit space that a battery cell can provide. One way to improve power-per-unit space is to reduce the size of the packaging or enclosure containing the electrolytic cell.
For extremely thin or unusually shaped batteries, flexible packaging has found advantageous application. Flexible packaging can provide hermetic containment of the battery, and in addition, has several advantages over traditional rigid metal or plastic packaging. Foremost, flexible materials are lighter and they can conform more easily to the shape of the battery structure, thus providing easier and more cost effective manufacturing.
The advantages of flexible laminate packaging are particularly valuable for small, high-energy batteries. In general, the smaller the battery becomes in any one dimension, the greater is the contribution of the packaging to the overall power per unit weight and/or power per unit volume of the battery.
The advantages of a flexible laminate packaging may be lost when packaging a non-aqueous battery, such as a high-energy lithium ion battery. If long storage and operating life are to be realized for such batteries, the packaging or enclosure must provide and maintain a hermetic barrier that will prevent electrolytic solvents from escaping from the battery and water vapor and oxygen from penetrating into the battery. Such a barrier is typically provided by a layer of metal foil within the flexible laminate. In order to maintain the hermetic barrier, it is also important that the laminate be formed into a bag or package without significant stretching or deformation of the laminate that may tear or rupture the metal foil layer.
FIGS. 1-5 show a conventional package configuration formed of a flexible laminate for an electrolytic battery. Typically, the packaging is formed from a flexible laminate having a polymer layer for toughness, a metal layer to form a hermetic barrier and an interior adhesive layer. The packaging is typically formed by placing a rectangular electrolytic cell onto one side of a sheet of the flexible laminate. The cell is positioned such that a portion of each of the leads extending from the cell is positioned on the laminate, and a portion of the leads extends beyond the edge of the laminate. The other half of the laminate sheet is then folded over onto the battery to overlay onto the other side of the sheet, with the interior adhesive layer in contact with itself along three peripheral edges where the laminate extends beyond the cell. In this respect, the laminate sheet is dimensioned such that when folded over, it extends beyond three peripheral edges of the cell. Heat and pressure are applied to these three edges to form a seal about the periphery of the cell.
As can be seen in FIG. 4, the sealed regions of the laminate that extend about the three sides of the cell occupy a significant amount of space. If the finished battery is intended to fit into a rectangular cavity within an electronic device, these sealed edges must be folded onto the cell body. The sealed side regions may be folded onto the cell body as illustrated in FIG. 5, but the front edge cannot be folded up without folding, tucking or wrapping the exposed portions of the sides. Such wrapping or tucking would result in several layers of the laminate being overlaid onto each other. Such a built-up region of overlapping laminate layers near the corner of the battery package is undesirable because it places considerable strain on the packaging laminate in the corner regions, which can distort the corners of the cell within the package. As a result, many batteries are used as shown in FIG. 5, with unused, dead space at one end of the battery where the leads extend therefrom. As will be appreciated, such unused space reduces the energy per volume that can be provided in a space allotted for a battery in an electronic device.
The present invention provides a package for a polymer battery that more efficiently utilizes space and provides a compact package having planar outer surfaces.
In accordance with the present invention, there is provided a package for a polymer battery. The package is comprised of a generally rectangular sheet of a packaging laminate having a cavity formed therein at one end of the sheet. The cavity is generally rectangular in shape and has a bottom, four sides and two truncated corners at two junctions where three of the four sides meet. The cavity is disposed in the sheet such that portions of the sheet define a flange that extends around the three of the four sides of the cavity. A portion of the sheet defines a cover that is folded along a fourth side of the cavity to overlay the flange. A seal is formed between the flange and the cover to hermetically seal the cavity. The flanges and the cover adjacent to the truncated corners are shaped to allow the flanges to be folded parallel to the three of four sides without overlapping.
In accordance with another aspect of the present invention, there is provided a battery comprised of a generally rectangular electrochemical cell having planar top and bottom surfaces and four sides. The electrochemical cell has two battery leads attached to current collectors extending from one side of the cell. A package formed from a sheet laminate has a cavity formed therein. The cavity has a bottom wall and four side walls that extend from the bottom wall to define an opening for receiving the cell and portions of the leads. A flange extends around the opening from at least three of the four side walls. A cover overlays the cavity and the flange. The cover is joined to the flange and forms a seal that hermetically seals the electrochemical cell within the cavity. The package has two, non-rectangular corners. The cover and the flange in the vicinity of the corners are shaped to allow the flange to be bent along the at least three sides wherein the flange is positioned adjacent the three sides, but the flange is not tucked or overlapped onto itself at the two, non-rectangular corners.
It is an object of the present invention to provide a package for small, electrochemical devices, wherein said package is formed of a flexible laminate material.
Another object of the present invention is to provide a method of packaging a prismatic, electrolytic battery with a flexible laminate material.
Another object of the present invention is to provide a method of packaging batteries as described above which maximizes the energy density of the battery.
Another object of the present invention is to provide a method of packaging batteries as described above that reduces the packaging space necessary for hermetically sealing the electrolytic cell.
A still further object of the present invention is to provide a method as described above that finds particular application in forming very thin batteries.
These and other objects will become apparent from the following description of a preferred embodiment taken together with the accompanying drawings.